Production method for a linear bearing

ABSTRACT

It is an object of the present invention to provide a linear bearing which is easy to manufacture and has sufficient mechanical strength, and its production method. A slider 1 guides a table or other movable bodies along a rail 2 and includes a thin ball plate 6 in which load ball channels 61 are formed to move balls 5 therein, and a thin mounting plate 7 adapted to secure the movable body. A molding material 8 such as resin or die cast alloy is molded to insert the ball plate 6 and the mounting plate 7 thereinto. The rail 2 is made of a metallic material 2 whose surface is hardened to a predetermined level when subjected to plastic deformation. During plastic deformation, the ball channels 23 are hardened to a predetermined level.

This is a divisional application of application Ser. No. 08/050,374,filed Jul. 16, 1993, now U.S. Pat. No. 5,380,099.

TECHNICAL FIELD

The present invention relates to a linear bearing for guiding movablebodies such as tables for use in various machine tools or industrialrobots along a straight bed or stationary element.

BACKGROUND ART

This kind of linear bearing comprises a rail having ball channels inwhich balls are moved and secured to a bed or stationary element, and aslider having load ball channels cooperating with the ball channels tosandwich a multiplicity of balls and adapted to guide a table or movablebody along the rail.

The slider has a function such that the load of the movable body isapplied directly thereto. Under the circumstances, if the slider isdeformed, the movable body is displaced relative to the base to whichthe rail is mounted. This presents a problem that the movable body cannot be guided accurately on a straight line. The slider body to whichthe movable body is secured must have high rigidity.

To thid end, the slider conventionally has a slider body formed from ametal block made, for example, of bearing steel. The slider body is madeby first cutting a rectangular metal block to a predetermined shape,then, forming nonload ball bores and tapping bolt holes for securementof a movable body, and finally, carburizing a portion of the slider bodyand cutting and lapping that portion of the slider body to form loadball channels.

However, where a slider body is made from a metal block made, forexample, of bearing steel, such a metal block must be machined invarious ways. This production method is thus cumbersome.

It is necessary to accurately and smoothly cut the slider body at apredetermined angle to form load ball channels. However, it is difficultto accurately contact a grinder or other cutting tools when the sliderbody has a complicated shape. This deteriorates the accuracy of loadball channels.

There is proposed a slider body made from materials other than metalblock. A thin metal plate has load ball channels and is molded, at itsouter periphery, of epoxy concrete or synthetic resin (see Japaneseutility model publication No. 48417/91).

According to this proposal, load ball channels can be readily andaccurately formed by pressing or ball burnishing the thin metal plate.Also, the slider body can readily be machined to a complicated shape.This slider body can be more economically made than those formed bymachining metal blocks.

However, the proposed slider body is less in rigidity than those madefrom metal blocks since it is like a metal plate with load ball channelsattached to a block made of synthetic resin. The slider body is thussusceptible to deformation or breakage when substantial load is exertedfrom a movable body.

A slider must have a mounting portion for securement of a movable body.Movable bodies have various shapes and are, therefore, secured to theslider in various ways. The mounting portion may be in the form, forexample, of a flange as an extension of the slider. Under thecircumstances, linear bearing manufacturers are required to providesliders with various mounting portions to meet user's need. Itsmanufacture is, however, rather cumbersome. Thus, there is a need forsliders which allow for ready securement of movable bodies in variousways and which are economical to manufacture.

Conventionally, a rail is formed by drawing a metal block to have apredetermined cross section, carburizing a portion of the metal block,and cutting or lapping that portion to form ball channels. Thisproduction method is as cumbersome as that of the slider. Anotherproblem is that the surface of the rail where balls are moved issusceptible to crack.

There has recently been proposed a rail which includes a thin metalplate in which ball channels are formed by press, and synthetic resininserted within the metal plate (see Japanese laid-open utility modelpublication No. 43521/90). However, to give ball channels predeterminedhardness, it is necessary to treat the metal plate with TUFFTRIDE orthermally treat the metal plate such as quenching to harden the surfacesof the ball channels on which balls are moved. This treatment is alsocumbersome and does not improve the fragility of the surfaces on whichballs are moved.

DISCLOSURE OF THE INVENTION

In view of these problems, it is an object of the present invention toprovide a linear bearing which is easy to manufacture and has highmechanical strength, and its production method.

In order to achieve the object, the present invention provides a sliderfor a linear bearing which comprises a thin ball plate having load ballchannels, and a thin mounting plate having mounting portions to which amovable body is secured, characterized in that the ball plate and themounting plate are integrated together by molding a molding materialsuch as resin or die cast alloy.

According to such technical means, the slide can be formed by injectionor extrusion molding synthetic resin within which the ball plate andmounting plate are inserted, or by die casting an alluminum or zincalloy. This allows for ready production of the slider having variousshapes such as an inclined C-shape or L-shape. The shape of the ballplate may thus be altered in response to the shapes of a slider. Also,the number and angle of load ball channels formed in the ball plate maybe changed as necessary.

The mounting plate may take any shape so far as it has mounting portionsto secure a table or other movable bodies. However, it is necessary forthe mounting plate to have high rigidity according to its shape andmaterial since the load of a movable body is applied locally to themounting plate.

Further, nonload ball channels can be any means applicable to theexisting linear bearings so far as it can bring balls up at ends of theload ball channels. In the present invention, for example, the sliderincludes nonload ball bores extending in parallel to the load ballchannels. End caps may be attached to front and rear ends of the sliderto provide a communication between the load ball channels and thenonload ball bores. Alternatively, ball tubes may be inserted in theslider to provide a communication between opposite ends of the load ballchannels.

The present invention has for its purpose to reduce the number ofproduction steps and the production cost. It is therefore preferable toform part of the nonload all channels during insert molding process.

The mounting plate is integrated in the slider by insert molding, butthe molding material such as resin surrounds the mounting plate, only.The mounting may be separated from the slider when substantial load isexerted on the mounting plate. To more firmly integrate the mountingplate in the slider, an adhesive agent may be applied to the mountingplate prior to insert molding. Alternatively, the ball plate and themounting plate may be projection welded or riveted together. However,the use of these means results in an increase in the number ofproduction steps and is not preferable as the purpose of the presentinvention is to reduce the production cost.

Therefore, the mounting plate preferably has a fixed portion which isembedded in the molding material during insert molding. This results ina decrease in the number of production steps simply by changing theshape of the mounting plate. The fixed portion may be in the form ofpawls provided at opposite ends of the mounting plate. Alernatively,recesses may be formed centrally in the mounting plate.

Where the mounting plate has a fixed portion, the fixed portionpreferably has an axial length less than that of the ball plate or hasthrough openings. This prevents separation of the molding materialcovering the fixed portion from the molding material surrounding theball plate and thus ensures firm integration of the mounting plate withthe ball plate.

The present invention also provides a rail for use in a linear bearingto achieve the foregoing object.

A first rail is made of a metallic material which has such acharacteristic that its surface hardness is increased when subjected toplastic deformation. The ball channels have predetermined surfacehardness when the rail is plastically deformed to a predetermined shape.

With these technical means, the rail is pressed or rolled to apredetermined shape where the rail is made from a thin metal plate. Atthat time, the surface of the ball channels is hardened to apredetermined level. The rail is drawn to a predetermined shape wherethe rail is made from a metal block. During drawing process, the surfaceof the ball channel is hardened to a predetermined level.

The surface hardness required for the ball channels may vary dependingon the material of balls and the load to be exerted on the slider, butis normally at least H_(R) C35. With this production method, the greaterthe deformation during plastic deformation, the greater the hardness ofthe ball channel surface on which balls are moved. Thus, where the railis made, for example, by drawing process, the surface hardness of theball channels can be adjusted by changing the volume as drawn by a dice.

The same production method is applicable to the ball plate of theslider. The surface of the load ball channels can be hardened to apredetermined level simply by pressing or rolling a thin metal plate toa predetermined shape.

To achieve the foregoing object, a second rail is made from a metal rodand includes ball channels which is subjected to quenching and subzero(or deep freezing) treatment.

With these technical means, the fragile metallic system is improvedduring quenching process to effectively prevent crack which may occur inthe ball channels upon repeated application of loads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a linear bearing according to a firstembodiment. FIG. 2 is a sectional view of the linear bearing accordingto the first embodiment. FIG. 3 is an exploded view, in perspective, ofthe linear bearing according to the first embodiment. FIG. 4 is aperspective view of the linear bearing according to the firstembodiment, part of which is taken away to show the structure of aslider body. FIG. 5 is a front view of the slider body of the linearbearing according to the first embodiment. FIG. 6 is a bottom plan viewof the slider body of the linear bearing according to the firstembodiment. FIG. 7 is a top plan view of the slider body of the linearbearing according to the first embodiment. FIG. 8 is a side view of theslider body of the linear bearing according to the first embodiment.FIG. 9 is a bottom plan view of an end cap of the linear bearingaccording to the first embodiment. FIG. 10 is a rear view of the end capof the linear bearing according to the first embodiment. FIG. 11 is asectional view taken along the line XI--XI of FIG. 10. FIG. 12 is afront view of the end cap of the linear bearing according to the firstembodiment. FIG. 13 is a sectional view taken along the line XIII--XIIIof FIG. 10. FIG. 14 is a sectional view showing a modified form of theslider of the linear bearing according to the first embodiment. FIG. 15is a perspective view of a linear bearing according to a secondembodiment, part of which is taken away to show the structure of aslider. FIG. 16 is a sectional view of the linear bearing according tothe second embodiment. FIG. 17 is a sectional view of the linear bearingaccording to the first embodiment, showing a modified form of a rail.

BEST MODE FOR CARRYING OUT THE INVENTION

A linear bearing and its production method of the present invention willnow be described with reference to the accompanying drawings.

FIGS. 1 and 2 show a linear bearing according to a first embodiment ofthe present invention. The linear bearing generally includes a rail 2,ad a slider 1 movable along the rail 2. FIG. 3 is a disassembled view ofthe slider 1 which includes a slider body 3 having a substantiallyinclined C-shape and extending over the rail 2, and a pair of end caps 4coupled to front and rear ends of the slider body 3. The slider 1 ismounted on the rail through balls 5 which endlessly circulate in theslider 1.

As shown in FIG. 4, the slider body 3 includes a channel-like ball plate6, and a mounting plate 7 having mounting portions 71 for mounting amovable body (not shown). The ball plate 6 and the mounting plate 7 areintegrally formed together by a synthetic resin 8 (for example,"TorayCA").

The ball plate 6 is made of stainless steel or other metal (for exmple,SUS430) and shaped by a press. Opposite inner surfaces of the ball plate6 form load ball channels 61 which cooperate with ball channels 23 ofthe rail 2 to sandwich the balls 5. Positioning projections 62 extendaxially from opposite ends of the ball plate 6 to position the end caps.The load ball channels 61 are quenched and then, subzero treated. Thistreatment hardens the load ball channels 61 to increase its resistanceto wear and stabilizes the metallic system of the load ball channels 61to improve its fragility.

Alternatively, a metal sheet whose surface hardness can be increasedwhen subjected to plastic deformation may be pressed or rolled to apredetermined shape. It is then plastically deformed to harden thesurface of the load ball channels 61 to a predetermined level. Such ametal sheet which can be used in this process is, for example, austeniteSUS304. The surface hardness of the load ball channels 61 is less thanH_(R) C10 prior to pressing and increased to H_(R) C35 to 40 after ithas been pressed. This method eliminates a need for heat treatment andresults in lower production cost.

The mounting plate 7 is formed also by pressing a sheet metal made, forexample, of stainless steeel and having a thickness slightly greaterthan that used for the ball plate 6. The mounting plate 7 includes arecess or fixed portion 72 embedded in the synthetic resin 8 and locatedbetween a pair of mounting portions 71. The mounting portions 71 aretapped to form bolt holes 73 for threading engagement with bolts (notshown) of a movable body. The axial length of the mounting plate 7 isshorter than that of the ball plate.

The slider body 3 is formed by insert molding the ball plate 6 and themounting plate 7. FIGS. 5 to 8 show the slider body 3 after it is insertmolded.

As is clear from these figures, the ball plate 6 is wrapped by syntheticresin and is not separated from the slider body 3 in any direction. Themounting portions 71 of the mounting plate 7 extend outwardly from thesurface of the slider body 3. The fixed portion 72 of the mounting plate7 is embedded in the synthetic resin 8. The mounting plate 7 is thus notseparated from the slider body 3 in any direction. During insertmolding, part of nonload ball bores is defined in the slider body 3 toprovide a connection between ends of the load ball channels to circulatethe balls 2 therethrough. Specifically, the slider body 3 has legs 31 inwhich ball bores 32 through which nonload balls are moved are defined inparallel relationship to the load ball channels 61. Semicircular returnguides 33 are formed in front and rear end surfaces of the slider body 3to direct the balls 5 from the load ball channels 61 and the ball bores32 and vice versa. Positioning holes 34 are defined during insertmolding to receive projections 41 of the end caps 4.

The slider body 3 is formed substantially during the insert moldingprocess. Finally, the mounting portions 71 of the mounting plate 7 whichextend outwardly from the surface of the slider body 3 is abraded toprovide a reference surface.

The end caps 4 coupled to front and rear ends of the slider body 3 areinjection molded of synthetic resin. Semicircular ball return channels42 are formed in the inner sides of the end caps 4 and form part of thenonload ball channels. As shown in FIGS. 9 to 13, the ball returnchannels 42 provide a connection between the load ball channels 61 ofthe slider body 3 and the ball bores 32. Tongues 43 extend from ends ofthe end caps 4 to bring the balls 5 up from the load ball channels 61.Also, seats 44 are provided centrally in the ball return channels 42 toreceive return guides 33 of the slider body 3 when the end caps 4 arecoupled to the slider body 3. This facilitates guidance of the balls 5through the ball return channels 42.

The end caps 42 are adhesively attached to the slider body 3. To ensureaccurate attachment of the end caps 4 to the slider body 3, the end caps4 have recesses 4 to receive projections 62 of the ball plate 6, andprojections 41 to fit into the positioning holes 43 of the slider body3.

As shown in FIGS. 2 and 3, the rail 2 includes a channel-like rail plate21 made by pressing, and a synthetic resin 22 inserted in the rail plate21 during molding process. A pair of ball channels 23 are formed inopposide outer sides of the rail plate 21 during pressing process. Also,through holes 24 are formed in the base along the length of the railplate 21. Bolt holes 25 are formed during insert molding process andcorrespond to the through holes 24. In this embodiment, the slider 1 hasno ball retainer. To avoid accidental removal of the slider 1 from therail 2 and disengagement of the balls 5 from the load ball channels 61,stoppers 9 are attached to opposite ends of the rail 2.

The surface of the ball channels 23 are hardened to a predeterminedlevel completely in the same manner as the load ball channels 61 of theball plate 6. After the rail has been pressed, the ball channels 23 arequenched and then, subzero treated. Alternatively, a metal sheet made ofaustenite SUS304 may be pressed or rolled to a predetermined shape tothereby increase the surface hardness of the ball channels 23 to apredetermined level.

When the slider 1 is in use, the balls 5 are placed in the nonload ballchannels composed of the ball return channels 42 of the end caps 4 andthe ball bores 32 of the slider body 3. The balls 5 are also placedbetween the ball channels 23 of the rail 2 and the load ball channels 61of the slider body 3. A movable body is then secured to the mountingportions 71 which extend outwardly from the upper surface of the slider1.

A substantial part of the slider 1 is formed of synthetic resin 8.However, part of the mounting plate 7 which has high regidity isembedded in the synthetic resin 8 to be integral with the slider body 3.This mounting plate 7 serves as a reinforcing element for the sliderbody 3 to increase the rigidity of the slider body 3. Thus, the sliderbody 3 is free from deformation or breakage if substantial load isexerted.

The mounting plate 7 and the slider body 3 are integrally formed duringinsert molding of the slider 3. A change in shape of the mounting plate7 results in a corresponding change in shape of the slider.

FIG. 14 shows a modification of the slider body 3 as insert molded. Theslider body includes a mounting plate 7a which has wider mountingportions than those of the mounting plate 7, and bolt holes 76.

According to this embodiment, while the ball plate 6 and other elementsare commonly used, a variety of mounting plates 7 can be employed toprovide a variety of sliders. Thus, various types of sliders caneconomically and readily be fabricated according to user's need.

In the foregoing embodiment, the axial length of the mounting plate 7 isless than that of the ball plate 6 so that the synthetic resin 8 whichcovers the fixed portion 72 of the mounting plate 7 are safely joined tothe synthetic resin 8 which surrounds the ball plate 6. As analternative, the axial length of the mounting plate 6 may be identicalto that of the slider body 3. In such a case, slots or through openings74 may be formed in the fixed portion 72 as shown in FIG. 15.

FIG. 16 is a sectional view showing a second embodiment of the slider 1wherein a mounting plate 7b has the through openings 74. As is clearfrom FIG. 16, the synthetic resin 8 which covers the fixed portion 72 ofthe mounting plate 7 through the through openings 74 is safely joined tothe synthetic resin 8 which surrounds the ball plate 6. This embodimentalso allows for firm integration of the mounting plate 7b with theslider body 3.

In this embodiment, the ball plate 6 is pressed, but the load ballchannels 61 are not abraded. However, the load ball channels 61 may needbe abraded when the plate 6 per se is made of a material which does notprovide a smooth surface.

The rail 2 in which the slider 1 of this embodiment is assembled may bemade by pressing a metal sheet. As shown in FIG. 17, a matal block maybe drawn to form a rail 2a of a predetermined shape. In such a case,ball channels 23a of the rail 2a are quenched and then, subzero treatedafter it has been drawn so as to increase resistance to wear and improvethe fragility of the ball channels 23a.

To reduce the cost of manufacturing the rail 2a, a block made ofaustenite SUS304 may be drawn to a predetermined shape. The rail 2a isplastically deformed to thereby increase the surface hardness of theball channels 23a to a preetermined level.

INDUSTRIAL APPLICABILITY

As described above, according to a linear bearing and its productionmethod of the present invention, a slider is formed by integrating ahigh rigid mounting plate with a ball plate by the use of moldingmaterial such as resin or die cast alloy. The slider thus made is highlyrigid even if molding material is relatively flexible. It is thereforepossible to provide a linear bearing which has high mechanical strength.

Also, according to a linear bearing and its production method of thepresent invention, a rail is plastically deformed to a predeterminedshape to thereby harden a ball channels. This eliminates a need for heattreatment of the ball channels. It is therefore possible to provide alinear bearing which has high mechanical strength and is economical tomanufacture.

Further, according to a linear bearing and its production method of thepresent invention, when a rail is quenched to harden ball channels,subzero treatment is subsequently effected to alter metallic system toimprove the fragility of the rail. The ball channels are thus free fromcrack. It is therefore possible to provide a linear bearing which hashigh mechanical strength.

I claim:
 1. A method of producing a linear bearing, said linear bearingcomprising a rail having ball channels, and a slider having load ballchannels cooperating with said ball channels to sandwich a multiplicityof balls and guiding a table or movable body secured to said slideralong said rail, said method comprising the steps offorming a thin ballplate having load ball channels, forming a thin mounting plate havingmounting portions to which the movable body is secured, and integrallymolding said ball plate and said mounting plate to provide said slider.2. A method of producing a linear bearing according to claim 1, whereinpart of nonload ball channels through which nonload balls are circulatedare formed when said ball plate and said mounting plate are integratedtogether during insert molding process.
 3. A method of producing alinear bearing according to claim 1, wherein said ball plate is madefrom a metal sheet whose surface hardness is increased when subjected toplastic deformation, and said load ball channels are hardened to apredetermined level while said ball plate is subjected to plasticdeformation.
 4. A method of producing a linear bearing, said linearbearing comprising a rail having ball channels, and a slider having loadball channels cooperating with said ball channels to sandwich amultiplicity of balls and guiding a table or movable body secured tosaid slider along said rail, said method comprising the stepsofproviding a metallic material whose surface hardness is increased whensubjected to plastic deformation, and plastically deforming saidmetallic material to form said rail and harden said ball channels to apredetermined level.
 5. A method of producing a linear bearing, saidlinear bearing comprising a rail having ball channels, and a sliderhaving load ball channels cooperating with said ball channels tosandwich a multiplicity of balls and guiding a table or movable bodysecured to said slider along said rail, said method comprising the stepsofforming ball channels in said rail, quenching said ball channels, andthen, subzero treating (or deep freezing) said ball channels.